1. Field of the Invention
This invention relates generally to transient elimination or suppression systems. More particularly, it relates to an electrical ground transient eliminator assembly for attenuating high frequency transients generated on an electrical load reference ground from being passed through to the AC power supply side of a system and for providing a safety relay, which, when energized due to excessive transients generated on the electrical load side of the system, allows the transients to safely bypass the continuous attenuator circuit and pass to earth ground.
2. Description of the Prior Art
In recent decades, much advancement has been made toward increasing the operating speeds of the electrical and electronic circuits within computer systems, cellular telephones and other such modern equipment. Along with the developments made in increasing operating speed, manufacturers have also been able to reduce the physical size of the circuits used in such equipment. In particular, this reduction in size allows manufacturers to add more and more circuits onto a particular integrated circuit chip. As the density of the integrated circuit chip increases with the addition of more circuits, it becomes increasingly more desirable to protect these low voltage chips from high voltage surges, transients, atmospheric discharges (i.e., lightning strikes), and electrical impulses that are induced into building electrical distribution. Other high energy transients may result from any number of other sources, as well, such as inductive or capacitive loads, including motors switching on/off, heat pumps, elevator controls, laser printers, computer disk drives, irrigation systems, solenoids cycling, and even the common telephone lines.
Every building structure, which is up to code, provides a common grounding presence for the many power supplies throughout the building. Particularly, these power supplies use the building electrical ground (earth ground) as a reference point for all of the voltages supplied to the electrical and electronic circuits (CPU, memory, hard disk, modem cards and security systems) in the equipment being used. This earth ground is tied directly to all of the system components for UL safety as well as for internal and external communication. On occasion, however, the earth ground may produce major problems for the equipment because the earth ground has the potential to create a control path for electrical interference which results in equipment damage, system failure and in many circumstances intolerable company “downtime.”
Although certain transient eliminator devices have been developed in the prior art to protect against transients generated on the ground wires of sensitive electronic circuits and/or security systems, these devices offer no protection against the overheating of the inductor coils of the transient eliminator device when an accidental short between the “hot” wire and the electrical load reference ground wire occurs at the load side. Because the prior art transient eliminator devices do not protect against this overheating problem, the short created by the accidental coupling of the “hot” wire and the ground wire would cause the fault current to flow in the ground wire, overheat the inductor coils of the transient eliminator device, increase the inductance of the device, which would slow down the reaction time of a circuit breaker in a distribution panel that is coupled to an external AC power source, and ultimately cause a fire.
In U.S. Pat. No. 6,385,029 to Donald G. Pennington issued on May 7, 2002, and entitled “Total Electrical Transient Eliminator”, which is assigned to the same assignee as the present invention, there is disclosed an apparatus for attenuating high frequency transients on AC power lines from damaging sensitive electrical and electronic circuits in an electrical load coupled to the AC power line. The AC power line has an earth ground and the electrical load has an electrical load ground. An isolation transformer is provided which has a primary winding and a secondary winding. The primary winding has a primary source lead, a primary neutral lead, and a primary electrostatic shield lead. The secondary winding has a secondary source lead, a secondary neutral lead, and a secondary electrostatic shield lead. The primary source lead, primary neutral lead, and primary electrostatic shield lead are electrically coupled to the AC power lines.
The secondary source lead, secondary neutral lead, and secondary electrostatic shield lead are electrically coupled to the electrical load. The primary electrostatic shield lead and the secondary electrostatic shield lead are electrically connected together and to the earth ground. A continuous attenuator circuit is used to attenuate high frequency transients in the frequency range of 50 kHz to 200 MHz electrically coupled between the earth ground and the electrical load ground. This '029 patent is hereby incorporated by reference in its entirety.
In U.S. Pat. No. 6,121,765 to Carlson issued on Sep. 19, 2000, there is disclosed an isolated electrical power supply. This '765 patent teaches an isolated electrical power supply for protecting electrical devices from transient voltages and currents. A filter is provided which includes a toroid and a resistor which are used in conjunction with an isolator transformer. The filter is coupled between the secondary neutral lead of the transformer and the secondary ground lead so as to shunt the current or voltage spikes. A ferrite bead is connected between earth ground and a binding post for filtering current in the 70-200 KHz range.
In U.S. Pat. No. 6,101,079 to Viklund issued on Aug. 8, 2000, there is disclosed a current and voltage transient protector. The protector module is designed for use with a wiring block having at least one wiring strip. The protector includes an insulative housing having disposed ends. At least four electrically conductive contacts are disposed in the housing. A first fuse is disposed in the housing and is electrically coupled between a first contact and a third contact, while a second fuse, also disposed in the housing, is coupled between a second contact and a fourth contact. An alternative embodiment discloses a first voltage surge suppressor being disposed in the housing and being coupled to a third contact, a second voltage surge suppressor also being disposed in the housing and being coupled to a fourth contact, and a ground contact being coupled to the first and second voltage surge suppressors.
Further, in U.S. Patent Application Publication No. 2003/0210104 to Nir et al. published on Nov. 13, 2003 there is disclosed an electromagnetic interference filter. The filter includes a core, which is mounted on a substrate, having at least one electrically conductive signal lead. The lead is surrounded by a first layer, which is made of glass-coated microwire. A tubular conductive material surrounds the first layer. The substrate is configured as a planar body, which has a top and bottom surface. Portions of the top and bottom surface are covered with electrically conductive material serving as signal and ground terminals and making electrical contact with the tubular conductive material of the core.
It would therefore be desirable to provide an electrical ground transient eliminator assembly, for attenuating high frequency transients generated on an electrical load reference ground from being passed through to the AC power supply side of a system, which includes a safety relay, which, when energized, allows excessive ground fault transients, caused by accidentally shorting a “hot” wire to the electrical load reference ground on the equipment side, to bypass the attenuator circuit of the assembly, pass safely to earth ground and, eventually, trip a circuit breaker located in a distribution panel that is coupled to the AC power supply side. It would also be expedient that the electrical ground transient eliminator assembly be easy to install and is formed of a mechanical package which can fit in a relatively small space.